1. Field of the Invention
The present invention relates to a space navigation optical instrument such as a space telescope mounted on an artificial satellite and, in particular, to a space navigation optical instrument in which a housing constituting an optical instrument is provided with a mechanism for discharging contaminants into the space and a contaminant removing method thereof.
2. Description of the Related Art
FIG. 6 is a cross sectional view showing a schematic structure of a space telescope as a conventional space navigation optical instrument. FIG. 6A shows the state where the space telescope is in advance of observations and FIG. 6B the state where the space telescope is in the process of observations in orbit. The space telescope is mounted on an artificial satellite going around the earth in a predetermined orbit.
Referring to FIGS. 6A, 6B, reference numerals 100a to 100c denote optical parts constructing the space telescope, which in the example shown in FIGS. 6A, 6B, constructs a reflecting optical system for receiving observed light B emitted from an observation object A. A reference numeral 101 denotes a lens barrel for housing therein the optical parts 100a to 100c, which protects the optical parts 110a to 100c from severe space environments such as heat, contaminants (for example, volatile substances and moisture generated in a vacuum environment from a CFRP structure (carbon fiber reinforced plastics) provided in the lens barrel 101, an organic material and the like) and radioactive rays. A reference numeral 102 denotes a top door mounted on an observation aperture (entrance pupil) for guiding the observed light B emitted from the observation object A to the optical parts 100a to 100c, which is supported by the lens barrel 101 by means of a hinge 103. The top door 102 is turned around the hinge 103 to allow the door 102 to be opened or closed. Further, a reference numeral 104 denotes a heat insulating material covering the lens barrel 101, which is a heat insulating material for the space called MLI (multi-layer insulation).
Next, the operation of the conventional space telescope will be described.
When the satellite mounted with the space telescope is launched and succeeded in going in a predetermined orbit, first, as shown in FIG. 6A, an optical axis of the optical system constructing the optical parts 100a to 100c of the space telescope is directed toward an optical axis of the observed light B emitted from the observation object A. Then, as shown in FIG. 6B, the top door 102 is opened to receive the observed light B by the optical parts 100a to 100c with started observations.
Here, for example, in the space telescope which receives light having a wavelength within a visible light range as the observed light B, the amount of heat absorbed by the mirror surface of the optical part of the reflecting optical system is determined by sunlight absorptivity (hereinafter referred to as “α value”). Variations in the amount of heat of absorption affects even the optical characteristics of a reflecting mirror. Thus, whether or not the space telescope satisfies performance requirements when it is operated in orbit depends on how degradation of the α value (increase in the α value) can be held down.
The degradation of the α value measured on the mirror surface of the optical part is caused mainly by adhesion of contaminants thereto. Further, when ultraviolet rays are irradiated on the mirror surface to which contaminants are being adhered, there may be the possibility that organic substances contained in the contaminants would be decomposed and blacked, bringing about a fatal malfunction in an optical telescope.
To eliminate such unfavorable malfunction, as control of the contaminants adhered to the mirror surface of the optical part, it is essential to quantitatively evaluate the control of the contaminants in every processes of manufacturing, assembling, testing and launching on the ground prior to launching an artificial satellite. Similarly, at the time of observations in orbit, it is vital to quantitatively evaluate the control of the contaminants.
The conventional space navigation optical instrument thus constructed as above precludes removal of the contaminants adhered to the mirror surface of the control part once the space navigation optical instrument is launched in space. This disable one from being coped with a malfunction caused by the contaminants.
Specifically, it can actually attend with very difficulties in quantitatively evaluating the control of the contaminants before the satellite is launched. For example, it precludes evaluation of the contaminants which are not generated under the atmospheric pressure but are vaporized when they are put in space under an ultra high vacuum. Further, in the first place, various kinds of adsorptive molecules such as water and the like are adhered to the mirror surface of the optical part under the atmospheric pressure, assuming a condition of the mirror surface significantly different from that in space.
On the other hand, it holds true as with predicting how many contaminants will be adhered to the mirror surface of the optical part during the period from the time immediately after the launching of the satellite to the time when the space telescope starts the observations in orbit. That is, the conventional space navigation optical instrument lacks means for quantitatively evaluating the amount of contaminant molecules generated in the lens barrel 101 or the amount of contaminants adhered to the mirror surface of the optical part during the period from the time immediately after the launching of the satellite to the time when the space telescope starts the observations in orbit.
Under such circumstances, if a conventional method of operating the space telescope as shown in FIGS. 6A, 6B is employed, the top door 102 comes to open, with the contaminants adhered to the mirror surface of the optical part. As a result, there will be many dangers that the space telescope cannot be made observations, depending on how large the α value degrades as well as the aforementioned malfunction occurs and thus the space telescope can not satisfy the performance requirements in the initial state of the observations.